Moisture indicator



Dec. 2, 1947. 's, F, 555m 2,431,742

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DRYING TRAIN FURNACE I INVENTOR Patented Dec. 2, 1947 UNITED STATES PATENT OFFlCE MOISTURE INDICATOR Sanford F. Essig, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application April 24, 1943, Serial No. 484,501

2 Claims. (CI. 73-29) This invention relates generally to moisture detectors and indicators and more particularly to an apparatus for detecting and indicating the presence of moisture in gases.

It is common practice in the heat treatment of metals to provide in the heating furnace a reducing atmosphere of a gas such as hydrogen. It has been found that the presence of moisture in the atmosphere within a heat treatment furnace causes oxidation and discoloration or blackening of the surface of certain alloys and especially chrome-iron alloys, such as stainless steel. This discoloration occurs at temperatures of the order of 1000 centrigrade when the dew point of the atmosphere is -20 centigrade or higher. Such discoloration is undesirable at all times and frequently cannot be tolerated, particularly with certain vacuum tube parts. Therefore, to prevent oxidation and discoloration, it is desirable to provide an apparatus for detecting the presence of moisture in hydrogen or even inert gases which may be supplied to a heat treating furnace during the process of heat treatment of chrome-iron cathode ray tube guns.

The principal object of this invention is to provide a novel apparatus for detecting and indicating the presence of moisture in a gas.

In accordance with the invention, there is provided a furnace adapted to create temperatures of the order of 1000 centigrade. A source of gas such as hydrogen and a gas-drying train is connected to the furnace for creating therein a dry atmosphere for preventing oxidation.

Between the drying train and the furnace, there is connected in the pipe line a device comprising a heated element of the same metal as that which is to be heat treated. If the dew point of the gas passing through the detection device is too high, the surface of the metal in the detection device will show discoloration. Such discoloration occurs on metals such as chrome alloys. In temperatures of the order of 1000 centigrade, the chromium will break down the moisture, which is present in the gas, into oxygen and hydrogen whereby chromium oxide forms on the surface of the metal and causes blackening of the surface.

For indicating the moisture content of the gas, there is provided a source of light for directing a beam of light onto the metal surface within the detection device and a photoelectric circuit responsive to the light reflected from that surface. The quantity of light reflected from the metal surface indicates the discoloration of the surface and the moisture content of the gas passing over that surface. An indicating means in the photoelectric circuit produces an intelligible indication of the moisture'content.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Fig. 1 of the drawings shows diagrammatically a system for supplying an inert gas to a furnace, together with a moisture detector, as provided in accordance with this invention; and

Fig. 2 is a cross-section view taken on line 2-2 of the moisture detecting device illustrated in Fig. 1.

Referring to Fig- 1 of the drawings, there is provided a furnace l which may be any one of the many types utilized in conventional heat treatment processes. For creating an atmosphere of inert gas within furnace I, there is provided a source-2 of inert gas such as hydrogen, a pipe connection 3, a drying train 4, a pipe connection 5 and a moisture detecting device 6.

The moisture detector 6 illustrated in Figs. 1 and 2 of the drawings consists of a transparent envelope 1 of glass, for example, to which may be attached the pipe 5 by means of connections 8 and 9. The envelope 1 is fixed at each end to holders H] which may include connections 8 and 9, as indicated. A ribbon ll of, for example, stainless steel or other chrome-iron alloy, is mounted on holders ID in any suitable fashion. There are provided the clips l2, for supporting the detector 6, connected, as illustrated in Fig. 1, to a source of electrical energy l4 and an indicating meter l5, whereby the ribbon Il may be heated to any desired temperature. There is also provided an adjustable resistor I! in circuit with source 14.

To cite a specific case, let it be assumed that certain parts of a cathode ray tube gun ordinarily made of chrome-iron alloy are to be heat treated in furnace l. The usual temperature of heat treatment is approximately 1000 centigrade and,

therefore, resistor H is adjusted to energize ribbon I l to heat it to a temperature of 1000" centigrade. Meter l5 may be calibrated to give a positive indication of the temperature of ribbon ll. Hydrogen gas may then be passed from source 2 through the drying train 4 and detection device 6 to the furnace I. If the dew point of the gas is in excess of 20 centigrade, ribbon II will show discoloration from oxidation and thereby indicate an excessive amount of moisture in the gas. In this event, it is only necessary to 3 dry the gas until the dew point is below 20 centigrade and preferably as low as 100 centigrade. The blackened or discolored ribbon has the characteristic that it may be re-generated by passing dry hydrogen over its surface so that the oxide film may be reduced and the surface will acquire its initial reflectivity constants.

The detection device 6 may be used as a moisture indicator by providing a source of light 20 which may be connected to any suitable source of potential such as battery 2|. For obtaining a predetermined light output from source 20, there may be provided an adjustable resistor 22. There is also provided a photoelectric cell 24 in position to intercept light reflected from the surface of ribbon I I. A suitable amplifier 25 may be connected to photoelectric cell 24 and in its output, there may be provided a meter 26 having a scale calibrated to indicate the moisture content of the gas passing over ribbon I l.

Thus, by providing a known amount of light from source 20, a certain degree of discoloration of the plate H produces a predetermined change in the reflection characteristic of the ribbon H and, therefore, photoelectric cell 24 produces an electrical output in direct proportion to the moisture content of the gas. Meter 26 thereby provides a positive indication of that moisture content.

From the above description of this invention, it is apparent that there is provided a simple and positive-acting device for indicating the moisture content of the atmosphere within a furnace. This invention presents the further advantage that the effects of the atmosphere within the furnace may be viewed directly in the indicating device through which the gas is passed. Therefore, it is possible to prevent damaging discoloration during heat treatment of objects within the furnace with certainty and without the use of cut and try methods.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A device for indicating the amount of moisture in a gas comprising a transparent envelope adapted to receive a gas, means for introducing a gas into said envelope, a metallic member supported within said envelope, and means for heating said metallic member to a predetermined temperature, said metallic member having the property, when its temperature is increased to a predetermined degree, of changing its external appearance in proportion to the amount of moisture surrounding the same.

2. A device for indicating the amount of moisture in agas comprising an envelope adapted to receive a gas, means for introducing a gas into said envelope, a metallic member supported within said envelope, means for heating said metallic member to a predetermined temperature, said metallic member having the property, when heated to a predetermined temperature, of chan ing its external appearance in proportion to the amount of moisture surrounding the same, a

source of light for directing a predetermined quantity of light onto the surface of said metallic member, and photosensitive means adapted to receive a quantity of reflected light from said metallic member in accordance with the external appearance thereof and to indicate said quantity of light as an index of the moisture content of the as.

SANFORD F. ESSIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,314,201 Elsey Mar. 16, 1943 2,280,617 Bell Apr. 21, 1942 1,941,128 Duval .1 Dec. 26, 1933 1,926,234 Harsch Sept, 12, 1933 1,960,658 Brace May 29, 1934 2,269,569 Williams Jan. 13, 1942 2,275,106 Hayes Mar. 3, 1942 2,191,133 Pearson Feb. 20, 1940 1,626,685 Marden et a1. May 3, 1927 2,316,624 Romanelli 1- Apr. 13, 1943 Re. 18,831 Fleisher May 16, 1933 1,697,454 Brown et a1 Jan. 1, 1929 2,257,487 Tenney Sept. 30, 1941 2,274,426 Miller Feb. 24, 1942 FOREIGN PATENTS Number Country Date 3,747 Great Britain Mar. 9, 1915 

